{
    // 声明
    let a1=Symbol();
    let a2=Symbol();
    console.log(a1===a2);//flase
    let a3=Symbol.for('a3');
    let a4=Symbol.for('a3');
    console.log(a3===a4);//true
}

{
    let a1=Symbol.for('abc');
    let obj={
      [a1]:'123',
      'abc':345,
      'c':456
    };
    console.log('obj',obj);

    for(let [key,value] of Object.entries(obj)){
        console.log('let of',key,value);
    }

    Object.getOwnPropertySymbols(obj).forEach(function(item){
        console.log(obj[item]);
      })
    
      Reflect.ownKeys(obj).forEach(function(item){
        console.log('ownkeys',item,obj[item]);
    })

}  